Aerodynamics

1
Aerodynamics
Getting to the Point
Orville Wright
Wilbur Wright
Written for the Notre Dame Pilot Initiative By
the Pilots of the University of Notre Dame
2
Four Forces of Flight

• Lift opposes Weight
• Thrust opposes Drag
• In straight, unaccelerated flight, L W T D

• Lift created by pressure differential around
  wing. High pressure on lower surface and low
  pressure on the upper surface low pressure
  caused by increased airflow velocity over top of
  airfoil.
• Weight downward force of gravity
• Drag rearward retarding force
• Thrust forward force propelling airplane
  through air

3
Airfoils

• What is NACA?
• National Advisory Committee for Aeronautics
• Chartered in 1915, operational from 1917-1958
• The National Aeronautics and Space Act of 1958
  created NASA from NACA

4
Aerodynamic Surfaces
5
Aerodynamic Surfaces
Prop
Jet
B727 Spoilers
6
Airfoils - Nomenclature
Low p
High p

• Chord line - straight line connecting the leading
  and trailing edges of an airfoil
• Camber line locus of all points equidistant
  from top and bottom of airfoil
• Camber distance between chord line and camber
  line
• Thickness maximum distance between top and
  bottom surfaces of wing
• Leading Edge
• Trailing Edge
• Wingspan (b)
• Aspect Ratio (AR b2/S)

7
Frost

• If wing is below dewpoint which is below
  freezing, frost will form
• Sublimation of air to solid ice crystals
• Disrupts smooth airflow over the wing

• Why is this bad?
• Decreases lift
• Increases drag
• Frost removed before take-off
• Rime Ice
• Clear Ice

8
Angle of Attack

• Angle between wing chord line and relative wind
• The angle of attack at which airplane stalls does
  not change

9
Published NACA Data NACA 2415
10
Airfoils - Nomenclature
11
Flaps
Plain Flap

• Flaps increase lift and decrease stall speed
• Flaps allow steep rate of descent for approaches
  without increasing airspeed

Split Flap
Fowler Flap
-Fowler Flap effectively increases the wing area
by rolling backwards on a roller system.
Slotted Flap
-Slotted Flap allows high pressure air underneath
wing to join airflow above wing. This effectively
increases velocity of top airflow and thus
increases lift.
12
Laminar v. Turbulent
Laminar flow about a sphere
13
Laminar v. Turbulent
Turbulent flow about a sphere
14
Bernoullis Principle - Lift

• As the velocity of a fluid increases, its
  internal pressure decreases.
• From Newtons 2nd (Fma)
• Shown by Venturi tube

Low Pressure
High Pressure
A1V1A2V2
15
Bernoullis Principle Again
Courtesy of FAA Pilots Handbook of Aeronautical
Knowledge, AC 61-23B
16
Bernoullis Principle Again
Courtesy of FAA Pilots Handbook of Aeronautical
Knowledge, AC 61-23B
17
Bernoullis Principle Again
Courtesy of FAA Pilots Handbook of Aeronautical
Knowledge, AC 61-23B
18
Lift Vector
Courtesy of FAA Pilots Handbook of Aeronautical
Knowledge, AC 61-23B
19
Drag Types

• Induced drag is the unavoidable by-product of
  lift and increases as the angle of attack
  increases
• Parasite drag is caused by any aircraft surface
  that deflects or interferes with smooth airflow
  around airplane
• Skin-friction drag - between the outer surfaces
  of the aircraft and the air through which it
  moves. Reduced by using glossy, flat finishes on
  surfaces
• Form drag - resistance of air to the shape of the
  aircraft. Form drag can be reduced by
  streamlining the aircraft shape.

20
Drag Body Comparison
sphere
cylinder
airfoil
21
Wingtip Vortices Twin Tornadoes
A few words on wingtip vortices
High pressure on the lower surface creates a
natural airflow that makes its way to the wingtip
and curls upward around it to the area of low
pressure. When flow around the wingtips streams
out behind the airplane, a vortex is formed.
These twisters represent an energy loss and are
strong enough to flip airplanes that blunder into
them.
22
Wingtip Vortices
23
Why Winglets?

• Equivalent to span extension w/o increased
  wingspan
• Reduces wingtip vortices
• Reduces drag

NASA B-727 Wingtip Vortex Test Flight
Learn more about winglets
http//www.airspacemag.com/ASM/Mag/Index/2001/AS/h
tww.html
24
Drag Ground Effect
TIP On a soft-field runway, you can takeoff at a
lower speed and then accelerate while in Ground
Effect.
25
Drag vs Angle of Attack
Relationship between drag and angle of attack
26
Torque / P-factor (Left-Turning Tendencies)

• Newtons 3rd law For every action there is an
  equal and opposite reaction.
• Propeller rotates CW when viewed from pilots
  seat.
• Torque reaction rotates the airplane CCW about
  longitudinal axis
• P-factor (asymmetrical thrust) caused by
  descending blade taking a greater bite of air
  than ascending blade at high angle of attack

27
Stability Control

• Inherently stable airplane returns to its
  original condition after being disturbed.
  Requires less effort to control

• Center of Gravity concerns
• Unable to compensate with elevator in pitch axis
• Weight and Balance becomes critical taught in a
  coming lecture

28
Stability Control
pitch

• The 3 axes of motion roll, pitch, yaw

roll
yaw
29
Tail Placements
Looks like the A-10 Also called H-Tail
30
Canards

• Stabilizer located in front of the main wings
• Used on the Wright Flyer
• More aerodynamically efficient than an elevator
  b/c canards provide positive lift

31
Accident Report Loss of Elevator

• AIRCRAFT FINAL REPORTTHE AIRCRAFT HAD JUST BEEN
  REPAIRED AFTER RECEIVING TORNADO DAMAGE. THIS
  REPAIR INCLUDED REMOVAL AND REPLACEMENT OF THE
  ELEVATOR CONTROL TUBE. THE PILOT TAXIED TO THE
  RUNWAY FOR THE PURPOSE OF A TEST FLIGHT. ALL
  FLIGHT CONTROL CHECKS APPEARED NORMAL. AFTER
  LIFT-OFF, THE PILOT INTENDED TO LEVEL OFF AT 5 TO
  10 FEET, THEN TOUCH DOWN AGAIN. HOWEVER, AFTER
  THE AIRPLANE BECAME AIRBORNE, HE LOST ELEVATOR
  CONTROL, AND THE AIRCRAFT CLIMBED STEEPLY TO 50
  TO 75 FEET. THE PILOT THEN REDUCED POWER, THE
  AIRCRAFT'S NOSE DROPPED, AND THE AIRCRAFT
  DESCENDED. WITH NO ELEVATOR CONTROL, THE PILOT
  WAS UNABLE TO ARREST THE DESCENT, AND THE
  AIRCRAFT IMPACTED THE GROUND. A POST-CRASH
  EXAMINATION REVEALED THAT A BOLT AND NUT WERE
  MISSING FROM THE ELEVATOR CONTROL LINKAGE, WHICH
  ALLOWED THE LINKAGE TO BECOME DISCONNECTED.
• AIRCRAFT 1 CAUSE REPORT FAILURE OF MAINTENANCE
  PERSONNEL TO PROPERLY REINSTALL A BOLT AND NUT IN
  THE ELEVATOR CONTROL LINKAGE, WHICH RESULTED IN A
  DISCONNECT OF THE LINKAGE AND LOSS OF ELEVATOR
  CONTROL.